Voltage-controlled oscillator and PLL circuit exhibiting high-frequency band operation, linear frequency characteristics, and power-source variation immunity

摘要

A voltage-controlled oscillator comprises a plurality of delay circuits connected in a ring configuration. Each of the delay circuits comprises a current source and a differential pair of inverting circuits each supplied with current from the current source. Each of the differential pair of inverting circuits consists of a P-type MOS transistor and an N-type MOS transistor having a drain connected to the drain of the P-type MOS transistor. When a control voltage equal to or higher than the threshold voltage of each N-type MOS transistor is applied to the gate thereof, the voltage at the drain of each P-type MOS transistor oscillates at a frequency corresponding to the control voltage, since each N-type MOS transistor exhibits a linear current characteristic with respect to the control voltage.